Some vehicle engine systems utilizing direct in-cylinder injection of fuel include a fuel delivery system that has multiple fuel pumps for providing suitable fuel pressure to the fuel injectors. As one example, a fuel delivery system can utilize an electrically driven lower pressure fuel pump (e.g., lift pump) and a mechanically driven higher pressure fuel pump arranged respectively in series between the fuel tank and the fuel injectors. The higher and lower pressure fuel pumps may be operated in conjunction to generate a desired fuel rail pressure during engine operation.
US 2009/0090331 discloses a fuel delivery system providing pressurized fuel to direct fuel injectors. The Inventors have recognized several drawbacks with the fuel delivery system disclosed in US 2009/0090331. For instance, the control scheme for the lower and higher pressure fuel pumps uses a pump model to determine the volumetric efficiency of the higher pressure that is sensitive to 1) manufacturing variability, 2) wear, and 3) direct injection (DI) pump inlet pressure. This prior algorithm depends on an a priori determination of “full DI pump volumetric efficiency”. Furthermore, the prior algorithm does not specifically put the DI pump inlet pressure at a high level to learn (i.e., self-calibrate) the volumetric efficiency associated with high DI inlet pressure. The time interval during which the pump efficiency is measured is not specified. During certain time intervals measuring the higher pressure fuel pump efficiency may be inaccurate. For instance, if the input to the higher pressure fuel pump is below a threshold value the pump efficiency measurement may not be accurate. Inaccuracies in volumetric efficiency measurements can lead to inefficient fuel delivery system operation.
The inventors have discovered a useful serendipity between controlling a lower pressure pump (e.g., lift pump) in pulsed mode and determining the higher pressure pump (e.g., DI pump) volumetric efficiency (e.g., maximum higher pressure pump volumetric efficiency). In one embodiment, each time that the lower pressure pump is operated at high pressure, the “best available” higher pressure pump volumetric efficiency can be measured and stored for us in detection of volumetric efficiency degradation (i.e., vapor detection). This self-learned calibration allows attribution of any degradation in higher pressure pump volumetric efficiency to the lowered lower pressure pump pressure. It will be appreciated that the lower pressure pump may be the higher pressure pump inlet pressure, in some examples. Thus, it may add robustness to the detection of low higher pressure pump volumetric efficiency and vapor detection. Prompt and reliable vapor detection enables a pulsed lower pressure pump in the fuel delivery system to be robust against unintended drops in fuel rail pressure (i.e., injection pressure).
As such in another embodiment, a method for operating a fuel delivery system for an engine is provided. The method includes sending a voltage above a threshold value to a lift pressure pump; and controlling the lift pump based on a volumetric efficiency of the direct injection pump determined only when the voltage sent to the lower pressure fuel pump is above the threshold value. In this way, an interval, which may be a time interval in one example, for determining volumetric efficiency of the higher pressure fuel pump is selected to provide an accurate efficiency determination. As a result, the likelihood of inaccurate pump efficiency measurements is decreased, thereby improving fuel delivery system operating efficiency.
In one example, sending the voltage above the threshold value to the lift pump is initiated responsive to implementation of a direct injection pump vapor detection routine. In this way, the volumetric efficiency determination and vapor detection routine can implemented at concurrent time intervals, thereby increasing the efficiency of the fuel delivery system.
Additionally in one example, it may be inferred that the lower pressure fuel pump pressure is greater than the threshold value when a predetermined voltage is applied to the lower pressure fuel pump for a predetermined time interval. In this way, the determination of the lower pressure fuel pump being above the threshold value is simplified.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified forth a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.